Another user who can record video but not sound. I'm using a kworld USB-USB2800D to capture old home video tapes of a Hi8 Sony handycam. The software that came with the capture device gets video and audio fine right out of the box, but drops the capther every few minutes randomly, stating the video is copy protected. So, I know the capture device is capable of getting sound to the capture file.
Now AVS video recorder gets the vidoe fine (it takes some tweaking, the 'reccomended format' choice won't work) but no sound. A little bit of checking shows the proper 'line-in' device is selected in the video recorder settings tab. Double checking at the Realtek HD Audio Manager (the on-board audio chip for this PC) showed that the volume for the line in device had both recording and playback volume muted. I put both back up and and tried to record again, and again, no sound. I re-opened the audio manager and both recording and playback volumes were again muted. Then I unmuted them, left the audio manager window open, and reopened AVS video recorder. As your video recorder opened, both playback and record volumes on the line-in device were both reset to mute.
If I reset the volume and start the capture, sound is captured. If I close the video recorder and re-open it, I have to reset the line-in volumes.
I can now get sound on the videos, but opening up that panel and un-muting the volumes is a pain. It looks like the video recorder is shooting itself in the head by muting the sound, causing you bunches of trouble. I looked for a setting in the realtek software that might be doing this, but could find no clue.
Though it might help, cheers.